Microarrays, bioinformatics and GMO risks and benefitsEdexcel International A Level Biology: Subtopic test

1. 1
   A researcher wants to know which genes are active in a breast tumour compared with healthy breast tissue. mRNA is extracted from each tissue and used to make cDNA labelled with a fluorescent dye: red for the tumour sample and green for the healthy sample. The labelled samples are mixed and added to a microarray, a slide on which each spot contains many copies of single-stranded DNA from one known human gene. After washing, the colour of each spot is recorded.

   (a)

   What allows the labelled cDNA to attach to a particular spot on the microarray?

   [1 mark]

   • ATranscription of the cDNA by RNA polymerase
   • BTranslation of the cDNA by ribosomes
   • CComplementary base pairing between the cDNA and the DNA at the spot
   • DHydrolysis of the cDNA by restriction endonucleases

   (b)

   One spot on the microarray fluoresces green only. What does this show?

   [1 mark]

   • AThe gene is transcribed in healthy tissue but not (or much less) in the tumour
   • BThe gene is transcribed in the tumour but not in healthy tissue
   • CThe gene is missing from the DNA of the tumour cells
   • DThe gene is present in the healthy tissue only, as a different allele

   (c)

   Explain why the researcher extracts mRNA, rather than DNA, from the tissues to find which genes are active.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A laboratory sequences the whole genome of a newly discovered soil bacterium. The team uses computer software and online databases of known gene sequences to look for genes similar to known antibiotic-resistance genes.

   (a)

   Which statement best describes bioinformatics?

   [1 mark]

   • AThe use of restriction endonucleases to cut genomes into fragments
   • BThe use of bacteria to make human proteins
   • CThe use of PCR to copy DNA
   • DThe use of computer software and databases to store, analyse and compare biological data such as DNA sequences

   (b)

   Why can bioinformatics help to predict the function of a newly sequenced gene?

   [1 mark]

   • ABecause any two genes of the same length code for the same protein
   • BBecause genes with similar base sequences in other organisms often code for proteins with similar functions
   • CBecause the position of a gene on the chromosome alone determines its function
   • DBecause identical sequences are only found within the same species

   (c)

   Suggest how bioinformatics could help the laboratory decide whether the bacterium may be resistant to antibiotics, and why this is quicker than testing the bacterium in the laboratory.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In a three-year field trial a GM maize variety carrying a gene from Bacillus thuringiensis for a toxin that kills the caterpillars of the maize borer was compared with a non-GM variety. The mean yield of the GM maize was 11.2 t ha⁻¹ and of the non-GM maize 9.8 t ha⁻¹. Farmers growing the non-GM maize sprayed insecticide on average 3.1 times per season; those growing the GM maize sprayed on average 0.5 times per season.

   (a)

   Explain how the use of the GM maize benefits farmers and the environment.

   [3 marks]

   (b)

   (i) Calculate the percentage increase in yield of the GM maize compared with the non-GM maize. Give your answer to 3 significant figures. (2 marks)
   (ii) Suggest two risks of growing this GM maize. (2 marks)

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A government is deciding whether to allow farmers to grow a GM rice that makes β-carotene (which is converted to vitamin A in the body) in its grains. Many children in the region have vitamin A deficiency. Some groups support the rice, while others are concerned about its effects on the environment and on farmers. Government scientists also want to check whether the genetic modification has caused unintended changes in the activity of other genes.

   (a)

   Evaluate the case for and against allowing farmers to grow the GM rice, and reach a justified conclusion.

   [6 marks]

   (b)

   Describe how a microarray could be used to find out whether the genetic modification has changed the activity of other genes in the rice, and explain how bioinformatics would help the scientists.

   [6 marks]

   Total for question 4: 12 marks

End of questions